This application claims the priority of German patent document No. 100 129 77.3-43, filed Mar. 16, 2001, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a method for bonding a sensor carrier plate to a vehicle window, in particular the windscreen of a passenger car or lorry. The present invention furthermore relates to an apparatus and its use for carrying out the above-mentioned method.
On modern passenger cars, a sensor array may be mounted on the windscreen, comprising, for example, a light sensor, a rain sensor, and a distance sensor. For this purpose, the sensor array or its components are mounted on at least one carrier plate that is secured on the windscreen by an adhesive joint. The carrier plate is provided on one side with an adhesive layer, which can be formed by a corresponding adhesive strip, for example. The adhesive layer must first of all be heated to form an adhesive joint with the windscreen. To prevent contamination of this adhesive layer, it is provided with a protective film that must be removed before the carrier plate is bonded to the windscreen. For the proper functioning of the optical sensor array, it is critical that the light path should not be obstructed by the carrier plate being bonded to the windscreen. In particular, craters, blisters, air inclusions and dirt in the adhesive layer and between the adhesive layer and the windscreen must therefore be avoided.
The conventional procedure for bonding a carrier plate is as follows. A carrier plate is taken manually from a storage bin and inserted into a furnace. In this furnace, the carrier plate and thus its adhesive layer are heated until the adhesive layer is sufficiently soft for bonding. The carrier plate is then removed manually from the furnace. The protective film must then be removed manually, after which the carrier plate is placed in a receptacle of a contact-pressure device. Finally, this contact-pressure device presses the carrier plate with its adhesive layer against the vehicle window for a predetermined time. The carrier plate is aligned parallel with the vehicle window before being pressed on, and is moved perpendicularly towards the vehicle window, with the result that the carrier plate and its adhesive layer come into full planar contact with the vehicle window, i.e. simultaneously by means of the entire adhesive layer.
Blisters may form in the adhesive layer even while heating is taking place in the furnace. Craters may form in the adhesive layer as the protective film is pulled off. Finally, air inclusions may occur as the carrier plate is brought into contact with the vehicle window. Overall, therefore, there is the risk that the light path through the adhesive layer will be obstructed and, as a result, it may be necessary to carry out expensive finishing work.
The present invention is concerned with the problem of designing a method such that the risk of an impaired light path through the adhesive layer is reduced.
The present invention is based on the general idea of bringing the carrier plate into contact with the vehicle window in a carefully controlled manner in such a way that the carrier plate with its adhesive layer is initially brought into point or linear contact with the vehicle window and only then into extended-area contact with the vehicle window, rather than being brought into contact in one plane. In this way, the air between the carrier plate and the vehicle window is displaced as the carrier plate is applied or brought into contact. The risk of air inclusions between the adhesive layer and the vehicle window is thereby reduced.
Contact is preferably made by a tilting movement and/or rolling movement between the carrier plate and the vehicle window, thereby reinforcing the above-mentioned displacement effect.
A further improvement is obtained in that an area of contact formed at the start of contact-making increases continuously in the direction of an outer edge surrounding the adhesive layer as contact making progresses. There is therefore a smooth transition between the point or linear initial contact and increasing extended-area contact and full, final contact over an extended area.
To improve a smooth transition between the point or linear initial contact and the full final contact over an extended area, the carrier plate and hence the adhesive layer can be bent reversibly in a convex manner towards the vehicle window for the purpose of making contact and bent back in the course of contact making. This ensures that the area of contact increases continuously in the course of contact making, rather than abruptly.
The heating of the adhesive layer by an appropriate heating device is expediently performed when the carrier plate is already in the contact-pressure device. This measure enables the method to be automated, thereby allowing the uniformity of the bonding process and hence its quality and reproducibility to be increased.
It is particularly advantageous if, before contact is made by the carrier plate with its adhesive layer, a vacuum is generated between the adhesive layer and the vehicle window. By this measure, air inclusions, which may form despite the special method of contact-making, are reduced in size by the ambient pressure prevailing after bonding. Given a vacuum of, for example, 200 mbar, the air inclusions shrink under ambient pressure to about ⅕ of their original extent. The method is preferably carried out at a vacuum of 10 mbar, as a result of which air inclusions are reduced under ambient pressure to about {fraction (1/100)} of their extent and are then generally so small as to be tolerable.
The problem underlying the present invention is also solved by an apparatus designed in such a way that the carrier plate with its adhesive layer initially comes into point or linear contact with the vehicle window. Immediately after this, the adhesive layer comes into extended-area contact with the vehicle window until full contact has been achieved. As described above, this reduces the risk of air inclusions while the carrier plate is being brought into contact with the vehicle window.
According to a preferred embodiment, a holding device, which holds fast the vehicle window to be provided with the carrier plate; a heating device, which heats the carrier plate, at least in the area of its adhesive layer; and a contact-pressure device, which has a receptacle for the carrier plate to be bonded to the vehicle window, can be mounted on a common stand. At least the receptacle of the contact-pressure device is mounted on the stand in such a way that it can be moved between a heating position and a contact-pressure position. The receptacle interacts in its heating position with the heating device to heat the adhesive layer of the carrier plate held therein. The receptacle interacts in its contact-pressure position with the holding device to press the carrier plate against the vehicle window. By virtue of the construction proposed, the apparatus is particularly suitable for automation of the bonding process, thereby simplifying the use of this bonding process in the context of large-scale manufacture.
It is self-evident that the features mentioned above and those that are mentioned below can be used not only in the respectively indicated combination but also in different combinations or alone without departing from the scope of the present invention.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing.